Add a new optional get_rx_ring_count callback in ethtool_ops to allow
drivers to provide the number of RX rings directly without going through
the full get_rxnfc flow classification interface.

Modify ethtool_get_rxrings() to use .get_rx_ring_count if available,
falling back to get_rxnfc() otherwise.

Signed-off-by: Breno Leitao <leitao@debian.org>
---
 include/linux/ethtool.h |  2 ++
 net/ethtool/ioctl.c     | 23 +++++++++++++++++++----
 2 files changed, 21 insertions(+), 4 deletions(-)

diff --git a/include/linux/ethtool.h b/include/linux/ethtool.h
index de5bd76a400ca..2d91fd3102c14 100644
--- a/include/linux/ethtool.h
+++ b/include/linux/ethtool.h
@@ -968,6 +968,7 @@ struct kernel_ethtool_ts_info {
  * @reset: Reset (part of) the device, as specified by a bitmask of
  *	flags from &enum ethtool_reset_flags.  Returns a negative
  *	error code or zero.
+ * @get_rx_ring_count: Return the number of RX rings
  * @get_rxfh_key_size: Get the size of the RX flow hash key.
  *	Returns zero if not supported for this specific device.
  * @get_rxfh_indir_size: Get the size of the RX flow hash indirection table.
@@ -1162,6 +1163,7 @@ struct ethtool_ops {
 	int	(*set_rxnfc)(struct net_device *, struct ethtool_rxnfc *);
 	int	(*flash_device)(struct net_device *, struct ethtool_flash *);
 	int	(*reset)(struct net_device *, u32 *);
+	u32	(*get_rx_ring_count)(struct net_device *dev);
 	u32	(*get_rxfh_key_size)(struct net_device *);
 	u32	(*get_rxfh_indir_size)(struct net_device *);
 	int	(*get_rxfh)(struct net_device *, struct ethtool_rxfh_param *);
diff --git a/net/ethtool/ioctl.c b/net/ethtool/ioctl.c
index a0f3de76cea03..4981db3e285d8 100644
--- a/net/ethtool/ioctl.c
+++ b/net/ethtool/ioctl.c
@@ -1208,6 +1208,23 @@ static noinline_for_stack int ethtool_set_rxnfc(struct net_device *dev,
 	return 0;
 }
 
+static int ethtool_get_rx_ring_count(struct net_device *dev)
+{
+	const struct ethtool_ops *ops = dev->ethtool_ops;
+	struct ethtool_rxnfc rx_rings = {};
+	int ret;
+
+	if (ops->get_rx_ring_count)
+		return ops->get_rx_ring_count(dev);
+
+	rx_rings.cmd = ETHTOOL_GRXRINGS;
+	ret = ops->get_rxnfc(dev, &rx_rings, NULL);
+	if (ret < 0)
+		return ret;
+
+	return rx_rings.data;
+}
+
 static noinline_for_stack int ethtool_get_rxrings(struct net_device *dev,
 						  u32 cmd,
 						  void __user *useraddr)
@@ -1217,7 +1234,7 @@ static noinline_for_stack int ethtool_get_rxrings(struct net_device *dev,
 	size_t info_size;
 	int ret;
 
-	if (!ops->get_rxnfc)
+	if (!ops->get_rxnfc && !ops->get_rx_ring_count)
 		return -EOPNOTSUPP;
 
 	info_size = sizeof(info);
@@ -1225,9 +1242,7 @@ static noinline_for_stack int ethtool_get_rxrings(struct net_device *dev,
 	if (ret)
 		return ret;
 
-	ret = ops->get_rxnfc(dev, &info, NULL);
-	if (ret < 0)
-		return ret;
+	info.data = ethtool_get_rx_ring_count(dev);
 
 	return ethtool_rxnfc_copy_to_user(useraddr, &info, info_size, NULL);
 }

-- 
2.47.3

On Fri, 12 Sep 2025 08:59:13 -0700 Breno Leitao wrote:
> @@ -1225,9 +1242,7 @@ static noinline_for_stack int ethtool_get_rxrings(struct net_device *dev,
>  	if (ret)
>  		return ret;
>  
> -	ret = ops->get_rxnfc(dev, &info, NULL);
> -	if (ret < 0)
> -		return ret;
> +	info.data = ethtool_get_rx_ring_count(dev);

Is there a reason we're no longer checking for negative errno here?
It's possible that none of the drivers actually return an error, but
we should still check. For consistency with the other patches / paths
if nothing else.

>  	return ethtool_rxnfc_copy_to_user(useraddr, &info, info_size, NULL);
-- 
pw-bot: cr

On Sun, Sep 14, 2025 at 12:59:49PM -0700, Jakub Kicinski wrote:
> On Fri, 12 Sep 2025 08:59:13 -0700 Breno Leitao wrote:
> > @@ -1225,9 +1242,7 @@ static noinline_for_stack int ethtool_get_rxrings(struct net_device *dev,
> >  	if (ret)
> >  		return ret;
> >  
> > -	ret = ops->get_rxnfc(dev, &info, NULL);
> > -	if (ret < 0)
> > -		return ret;
> > +	info.data = ethtool_get_rx_ring_count(dev);
> 
> Is there a reason we're no longer checking for negative errno here?
> It's possible that none of the drivers actually return an error, but
> we should still check. For consistency with the other patches / paths
> if nothing else.

Agree, we need to check the result of ethtool_get_rx_ring_count, and
return it if negative. I will update the patchset.